Potential of cereal grains and grain legumes in modulating pigs׳ intestinal microbiota - A review

Dietary modulation seems to be a promising tool to promote growth and activity of the beneficial members of the indigenous intestinal microbiota in monogastric animals such as pigs. Several approaches, including the use of various feed additives such as pro- and prebiotics have proven to be efficient in modulating pigs׳ intestinal microbiota. Furthermore, ingredients of a typical pig diet such as cereal grains contain considerable amounts of fermentable carbohydrates including e.g. resistant starch, mixed-linked β-glucan or arabinoxylan, which can serve as substrates for bacterial fermentation in the gastrointestinal tract. Thus, research has been increasingly focusing on the potential of fermentable carbohydrates present in cereal grains to steer intestinal microbial activity and composition in a beneficial way. In this review, special interest will be directed to wheat and barley due to their frequent use as main ingredients in pig diets, in addition to rye and oat, as these grains are known to contain considerable amounts of fermentable carbohydrates. Furthermore, the potential of grain legumes including peas, faba beans and lupins in beneficially modulating pigs׳ intestinal microbiota and activity will also be assessed as these feed ingredients contain not only varying amounts of protein but also different contents of various fermentable carbohydrates. This review includes a comparison of studies, in which either whole cereal grains and grain legumes or purified carbohydrate fractions manufactured from these grains were included in pigs׳ diets to study their effect on intestinal microbiota and metabolic activity. It also takes into account variations between several cereal genotypes, as content and composition of fermentable carbohydrates may not only vary between grains, but also between different genotypes of the same grain species. Finally, results of in vitro studies will be presented to assess the potential of fermentable carbohydrates originating from cereal grains and grain legumes in modulating microbial composition activity in a beneficial and health promoting way.